Alarm has grown since the World Health Organization (WHO) on Monday declared Zika an international health emergency that could infect as many as 4 million people in the Americas.

Zika is carried by mosquitoes, which transmit the virus to humans, while two cases in the United States suggest it may also be transmitted sexually.

The symptoms, which can include fever and skin rash, are typically mild. But health officials are most concerned by its potential link to microcephaly, a birth defect in which babies are born with abnormally small heads and underdeveloped brains.

Though the link hasn’t been proven yet, some athletes are rethinking their plans for the Rio Olympics, which get underway on Aug.5. Many others say they will take precautions but won’t let a low risk of infection blur their focus.

“The way I see it, it’s better to die for an Olympic gold than be scared and sit at home,” Indian shooting coach Ronak Pandit told Reuters in a phone call from his Mumbai home.

Pandit, a former shooter, now coaches his dentist wife Heena Sidhu, who last month earned her Rio place in air pistol shooting.

“The idea would be not to get bitten by mosquitoes,” she said. “Use mosquito repellent or nets, go out only in full-sleeve clothes, that kind of thing. I‘m not changing my preparation. I‘m not really thinking about it.”

Danish sailor Anne Marie Rindom is also unperturbed. “I’ll just buy some really strong insect repellent,” she said. “That’s how much I’ve thought about it. I‘m not worried about it.”

Plenty are concerned, though.

“From what I have seen and heard, if you are a pregnant woman it is very dangerous,” U.S. sprinter Justin Gatlin told Reuters.

Gatlin, an Olympic and World Champion sprinter, said he would likely avoid Brazil ahead of the Games but the lure of the Olympics themselves would likely prove too strong.

“At this point in time, if I had to take the risk about the virus, I am going to take it,” he said. “I am trying to capture my victory and my glory at the Olympics. Hopefully the Zika virus will be more contained by August.”

RISK DEBATE

Pre-Olympic trials are scheduled in Rio ahead of the August Games and the IOC says the Games will take place during the winter months when a drier, cooler climate reduces the presence of mosquitoes and risk of infection.

Scientists say that developing a vaccine for Zika could take years and, while the IOC says there have been no discussions about cancelling or postponing the Games, some medical experts say that is exactly what should happen.

“The Rio Games ought to be deferred,” Arthur Caplan, Director of the Medical Ethics program at the New York University Medical Center, told Reuters.

“The Games are important, but they are games and that’s not as important as a major health problem,” said Caplan, who has worked with WHO on ebola and pandemic flu ethics committees.

Brazil expects as many as 380,000 tourists to visit Rio in August and Caplan said there was a risk some could spread the virus to new areas once they return to home.

But Chris Barker, a specialist in mosquito-borne illnesses, told Reuters it was too early to make any decision to cancel the Games. Experts could not accurately predict the Zika situation in six months’ time while the seasonal factors and Rio’s commitment to intensive mosquito control meant travellers’ risk of contracting Zika was “probably very low.”

Nevertheless, he said ‘at risk categories’ should be prudent: “If I were a women who was pregnant or might become pregnant I would not travel to the Games,” Barker said.

SCIENTIFIC EVIDENCE

Brazil is investigating Zika’s possible links to more than 4,000 suspected cases of microcephaly among newborns. Researchers have identified evidence of Zika infection in at least 17 of these cases, either in the baby or in the mother, but have not confirmed a causal link to Zika.

Researchers in northeastern Pernambuco state reported on Wednesday that they found Zika antibodies in 12 babies with microcephaly. Barker said that suggested that further research was more likely to confirm the Zika link to microcephaly.

Some sports federations say their athletes are yet to express any fears and that they trust the organisers.

“We had our test event in Rio days ago and everybody came back safe and alive,” United World Wrestling president Nenad Lalovic told Reuters.

“There is big concern... but I do not think it is as serious as it is presented. We will be there in the winter and that gives us an advantage. In the past we had so many threats of epidemics, bird flu, chicken flu and nothing happened.”

International swimming federation FINA Executive Director Cornel Marculescu told Reuters no concerns had been voiced by national swimming federations.

British rower Andrew Triggs Hodge is taking action, however.

A gold medallist in Beijing in 2008 and London four years later, the 36-year-old is going for a hat-trick of golds in Rio, but he will be alone after he and his wife Eeke decided she would stay at home.

“For anybody who wants a family, Zika is a very real and frightening threat,” he told Britain’s Times newspaper. He said some research suggested women infected with Zika should wait two years before trying for children.

“It’s not a price worth paying,” he said. “I’ve been asking about mosquito nets, but if you’re there for seven days you’re going to get bitten.” (Additional reporting by Amlan Chakraborty in New Delhi; Gene Cherry in Raleigh, Durham; Karolos Grohmann in Berlin; Nikolaj Skydsgaard in Copenhagen; Editing by Jon Boyle)